tutoring till5

• Membrane Structure:

  • Phospholipids arranged in a bilayer
  • Globular proteins inserted in the lipid bilayer
  • Fluid mosaic model: proteins are floating in the membrane
• Factors influencing fluidity of the membrane:

  • Saturated fatty acids make the membrane less fluid than unsaturated fatty acids
  • Warm temperatures make the membrane more fluid than cold temperatures
  • Lipid composition of the ER membrane, Golgi stack & plasma membrane are distinct
• Cell Membrane:

  • Freeze-fracture allows a cell to be cleaved between the lipid bilayer, splitting the plasma membrane into two layers
  • Components of cellular membranes: phospholipid bilayer, transmembrane proteins, interior protein network, and cell surface markers
• Cell Membrane Components:

  • Integral proteins pass through the plasma membrane with nonpolar regions attaching to the lipid bilayer
  • Carbohydrate chains are often bound to the extracellular portion of proteins, forming glycoproteins
  • Peripheral membrane proteins bind to integral proteins or lipids on the surface of the membrane
  • Glycolipids are lipids modified by adding a sugar
• Phospholipid Structure:

  • Consists of glycerol, two fatty acids, and a phosphate group
  • Phospholipid bilayers are fluid and influenced by factors like fatty acid saturation, temperature, and lipid composition
  • Anchoring molecules are modified lipids bound covalently to integral proteins
• Detailed Summary:

  • Integral membrane proteins span the lipid bilayer with nonpolar regions embedded in the interior
  • Transmembrane domains consist of hydrophobic amino acids in alpha helices
  • Extensive nonpolar regions in transmembrane proteins can create a pore through the membrane (beta-barrel)
• Passive Transport:

  • Movement of molecules through the membrane without requiring energy, following the gradient
  • Diffusion: movement from high to low concentration until equilibrium is reached
• Facilitated Diffusion:

  • Allows molecules that cannot easily cross the membrane to move through membrane proteins like channel proteins and carrier proteins
  • Ion channels allow the passage of ions through the nonpolar interior of the plasma membrane
• Permeability Summary:

  • Nonpolar molecules move until concentration is equal on both sides
  • Limited permeability to small polar molecules
  • Very limited permeability to larger polar molecules and ions
• Carrier Proteins:

  • Transport ions and other solutes like sugars and amino acids
  • Movement occurs via diffusion and requires a concentration difference across the membrane
• Osmosis:

  • Movement of water across a membrane from lower to higher solute concentration
  • Involves hypertonic, hypotonic, and isotonic solutions
  • Aquaporins are specialized channels for water movement
• Solutes and Osmotic Pressure:

  • Osmotic pressure is the force needed to stop osmotic flow
  • Cells in hypotonic solutions gain water, causing them to swell
  • Different cells have mechanisms to deal with osmotic pressure
• Maintaining Osmotic Balance:

  • Single-celled eukaryotes use extrusion through contractile vacuoles for water ejection
  • Marine organisms adjust internal concentration to match seawater
  • Plant cells use turgor pressure to keep the cell rigid
• Active Transport:

  • Requires ATP for energy
  • Moves substances from low to high energy/concentration against the gradient
  • Uses highly selective carrier proteins like uniporters, symporters, and antiporters
• Sodium-Potassium (Na+/K+) Pump:

  • Uses ATP for active transport
  • Moves 3 Na+ out of the cell and 2 K+ into the cell against their concentration gradient
• Endocytosis and Exocytosis:

  • Endocytosis: movement of substances into the cell (phagocytosis, pinocytosis, receptor-mediated endocytosis)
  • Exocytosis: movement of substances out of the cell
• Questions:

  1. The lipid layer that forms the foundation of cell membranes is primarily composed of molecules called ________.
  2. phospholipids
  3. fats
  4. proteins
  5. carbohydrates
• 1. While water continually orients phospholipids into a lipid bilayer, it does not fix the lipids permanently into position. Thus, the bilayer is considered to be ________.
  2. fluid
  3. static
  4. fluctuating
  5. charged
• 1. What describes the movement of substances down their concentration gradients?
  2. Diffusion
  3. Active transport
  4. Saturation
  5. Bulk transport
• 1. Osmosis is the diffusion of water across a membrane in response to the concentration of one or more of the ________.
  2. solutes
  3. membranes
  4. compartments
  5. cells
• 1. Which type of proteins is embedded in the cell membrane in both active transport and facilitated transport?
  2. carrier
  3. cytoskeletal
  4. structural
  5. targeted
• 1. Osmosis occurs as water can cross the lipid bilayer through specialized channels for water movement called ________.
  2. aquaporins
  3. proteins
  4. membrane pores
  5. transmembrane carbohydrates
• 1. The plasma membrane is a thin sheet of lipid embedded with ________.
  2. proteins
  3. carbohydrates
  4. polymers
  5. nucleotides
  6. sodium and potassium ions
• 1. Membrane proteins are not very soluble in water because they possess long stretches of non-polar amino acids that are ________.
  2. hydrophobic
  3. too long to interact with the water molecules
  4. transmembranal
  5. hydrophilic
  6. used as transport channels
• 1. If a cell has the same concentration of dissolved molecules as its outside environment, the cell's condition is referred to as being ________.
  2. isotonic
  3. hypertonic
  4. hypotonic
  5. hydrophobic
  6. hydrophilic
• 10) A type of transport of a solute across a membrane, up its concentration gradient, using protein carriers driven by the expenditure of chemical energy is known as ________.

  1. active transport
  2. osmosis
  3. diffusion
  4. facilitated transport
  5. exocytosis
• 12) How are the tails and heads of membrane phospholipids oriented in their environment?

  1. The hydrophobic heads are oriented toward each other and the hydrophilic tails are oriented toward the extracellular fluid and the intracellular fluid
  2. The hydrophilic tails are oriented toward each other and the hydrophobic heads are oriented toward the extracellular fluid and the intracellular fluid
  3. The hydrophobic tails are oriented toward each other and the hydrophilic heads are oriented toward the extracellular fluid and the intracellular fluid
  4. The hydrophilic heads are oriented toward each other and the hydrophobic tails are oriented toward the extracellular fluid
• 13) What is the major barrier to crossing a biological membrane?

  1. Hydrophobic interior
  2. Hydrophilic exterior
  3. Protein channels
  4. Carbohydrate chains
• 14) What is the function of facilitated diffusion?

  1. Allows molecules to move through membrane proteins
  2. Requires energy to move molecules
  3. Moves molecules against their concentration gradient
  4. Forms a hydrophobic passageway through the membrane
• 15) What is the force needed to stop osmotic flow called?

  1. Osmotic pressure
  2. Hydrostatic pressure
  3. Turgor pressure
  4. Osmotic potential
• 16) How do marine organisms adjust to osmotic pressure?

  1. By circulating isotonic fluid
  2. By using turgor pressure
  3. By maintaining an isotonic environment
  4. By extruding water through contractile vacuoles
• 17) What type of transport requires ATP for energy and moves substances against their concentration gradient?

  1. Active transport
  2. Facilitated diffusion
  3. Osmosis
  4. Passive transport
• 18) What is the function of the sodium-potassium pump?

  1. Moves 3 Na+ into the cell and 2 K+ out of the cell
  2. Moves 3 Na+ out of the cell and 2 K+ into the cell
  3. Maintains an isotonic environment
  4. Requires energy for passive transport
• 19) What is the process that involves the movement of substances out of the cell?

  1. Exocytosis
  2. Endocytosis
  3. Phagocytosis
  4. Pinocytosis
• 20) What is the term for the movement of substances into the cell?

  1. Endocytosis
  2. Exocytosis
  3. Facilitated diffusion
  4. Active transport
• 21) What type of proteins assist in facilitated diffusion by forming a hydrophilic passageway through the membrane?

  1. Channel proteins
  2. Carrier proteins
  3. Integral proteins
  4. Peripheral proteins
• 22) What is the movement of substances down their concentration gradient without requiring energy called?

  1. Diffusion
  2. Active transport
  3. Osmosis
  4. Bulk transport
• 23) What is the term for the movement of water across a membrane from a lower to a higher solute concentration?

  1. Osmosis
  2. Diffusion
  3. Facilitated diffusion
  4. Active transport
• 24) What are the specialized channels for water movement in the cell membrane called?

  1. Aquaporins
  2. Proteins
  3. Transmembrane carbohydrates
  4. Membrane pores
• 25) What is the term for the force needed to stop osmotic flow?

  1. Osmotic pressure
  2. Hydrostatic pressure
  3. Turgor pressure
  4. Osmotic potential